1. Field of the Invention
This invention relates generally to planar magnetron sputtering devices and more particularly to a planar magnetron sputtering device with a moving magnetic field to provide greater and more uniform utilization of the target sputtering material and uniform deposition on a substrate.
2. Description of the Prior Art
Devices by which substrates are coated by a sputtering process are well known. A target material subject to a magnetic field is placed in an inert gas environment in proximity to a substrate and a DC or RF voltage is applied, resulting in the transfer of target material from the target to the substrate. Since the development of this technology it has been an objective to increase the utilization of target material. Targets are made from expensive metal and any means by which more of that metal can be used for sputtering before the target must be replaced is desirable and economical. Beyond the expense of the targets themselves is the lost production time while the sputtering process must be terminated for target replacement. By increasing the life of a target the lost production time can be minimized.
It is well known that maximum erosion of a target occurs where lines of magnetic flux are parallel with the surface of the target. The magnetic flux is provided by magnets located in proximity to the target. Magnetic lines of flux typically form closed loops extending from one pole of a magnet to the opposite pole. Where the magnetic field remains stationary during the sputtering process the maximum erosion of the target takes the form of a groove in the target. Typically, such grooved erosion patterns are in the form of a race track, but depend on the location of the stationary magnets with respect to target surface. One example of an attempt to increase target utilization is disclosed in U.S. Pat. No. 3,956,093 issued to Paul S. McLeod. McLeod discloses a second magnetic field normal to a first magnetic field to flatten the shape of the flux pattern, thereby having lines of flux parallel to the target surface over a greater portion of that surface.
Other attempts to flatten the flux pattern over the target are found in U.S. Pat. Nos. 4,312.731 and 4,162,954 issued to Charles F. Morrison. Additionally, U.S. Pat. Nos. 4,175,030 and 4,116,806 issued to Robert B. Love, et al. disclose other approaches to solving the target erosion pattern problem. However, none of the prior art mentioned above discloses movement of the source of the magnetic field to accomplish their goals. While improving target utilization, the prior art devices still are characterized by target erosion patterns which resemble a groove running over the surface of the target. Typically, only forty to fifty percent of the target material is used before it must be replaced.
Where grooved erosion patterns occur, there is a risk that the entire thickness of the target will be exhausted at the bottom of the groove, thereby contaminating the substrate with the material on which the target is mounted. Therefore, it may be safe to only use approximately forty percent of the target in order to avoid the contamination problem. In some instances, the target is bonded to its mounting plate. The bonding process is fairly expensive and this expense increases as the frequency of target replacement increases.